1. Field of the Invention
The present invention relates to a conveying device that conveys a recording medium and an image forming apparatus that includes the conveying device.
2. Description of the Related Art
For example, Japanese Patent Application Laid-open No. H5-134499 and Japanese Patent Application Laid-open No. 2006-1686 disclose a conventional conveying device that conveys a recording medium with an unfixed image to a fixing unit of an image forming apparatus. Copiers and printers are examples of such an image forming apparatus.
In a typical image forming apparatus, an image carried on an image carrier such as an intermediate transfer belt is transferred onto the recording medium at an image transfer unit. The recording medium on which the unfixed image is carried is conveyed to the fixing unit by a conveying belt, which is a part of the conveying device. After the image on the recording medium is fixed by the fixing unit, the recording medium is discharged outside the image forming apparatus. When the conveying belt conveys a recording medium, measures are taken so that the recording medium adheres to the conveying belt. Such measures include absorbing air through a plurality of suction holes (air holes) arranged in the conveying belt so that the recording medium firmly adheres to the conveying belt due to suction force. Because the recording medium firmly adheres to the conveying belt, image distortion is prevented that could be caused because the unfixed image on the recording medium is scraped against parts of the conveying path.
Japanese Patent Examined Publication No. H4-13265 discloses a conventional technology in which minute asperity is formed on a surface of a conveying belt to enhance its frictional properties with respect to recording media.
In the conventional technology, however, uneven gloss may be caused on an image in the fixing process due to the presence of portions with and without the suction holes in the conveying belt.
The inventor has led to the following results after a strenuous study to address the above problems.
First, the chances of occurrence of uneven gloss are higher when an inner peripheral surface of the conveying belt is located significantly away from a guiding member. In other words, in the conventional conveying devices, a large opening (communicated to a suction path formed by a suction fan) is arranged below a conveying surface of the conveying belt to absorb air through the suction holes. Due to the presence of such a large opening, the inner peripheral surface of the conveying belt is located significantly away from a guiding member, thereby increasing the chances of occurrence of uneven gloss.
In addition, uneven gloss is also caused when the recording medium comes into close contact with the suction holes. In the conventional conveying devices, because air is sucked through the suction holes, the recording medium comes into close contact with the suction holes, thereby increasing the chances of occurrence of uneven gloss.
Based on the above discussion, the inventors concluded that uneven gloss is generated due to a change in the potential of an image carried on a recording medium at the positions of the suction holes.